1. Field of the Invention
The present invention generally relates to exhaust systems and more particularly to marine wet exhaust systems which prevent the flow of engine exhaust gases back into marine vessels.
2. Prior Art
Most marine exhaust systems are subject to a serious problem, namely, that of permitting the gases exhausted therefrom to flow back into the rear of the vessel. This is particularly the case with power cruisers and motor sailboats in which the rear of the vessel is not fully enclosed. Thus, as such a vessel moves forward through the water, a turbulent boundary layer of air flows along the sides of the vessel. Moreover, the area just to the rear of the vessel becomes a low pressure area. Exhaust gases ejected along the sides or at the rear of the vessel are drawn into this area due to its low pressure and easily pass from this area into the open rear of the boat, endangering and inconveniencing the boat's occupants. This effect is known as the "station wagon" effect, since it also occurs in auto station wagons and normally precludes their rear windows from being open while they are being driven forward. Exhaust gases ejected to the rear of the boat also easily pass into the boat when the boat backs up in the water so that the phenomenon is present, regardless of the direction of the boat.
Previous attempts to prevent the station wagon effect in marine vessels have largely consisted either of exhausting engine gases from the sides or rear of the boat through piping of extended length, or of exhausting the engine gases to the rear of the boat and well below the surface of the water. Neither solution has been suitable. Thus long pipe extensions are difficult to support and are subject to damage by dock structures, other boats, or severe wave action. Moreover, they preclude very close-in maneuvering of the vessel on the side or rear from which the piping extends, which is at the least an inconvenience. Underwater exhaust systems tend to create excessive exhaust gas back pressures and thus may seriously interfere with engine efficiency. Moreover, they usually are somewhat ineffective, to prevent the station wagon effect.
Accordingly, there is a need for a simple, durable, inexpensive but highly effective marine exhaust system which will prevent the station wagon effect without interfering either with engine performance or with vessel maneuverability and without providing other drawbacks.